Some techniques have been proposed for detecting a pressure within a combustion chamber (referred to as an in-cylinder pressure) of a internal-combustion engine (referred to as an engine) to calculate engine work such as an indicated mean effective pressure based on the detected pressure and a rate of change in the stroke volume of the combustion chamber.
Japanese Patent Application Publication listed below discloses a technique for deriving an equation to be used for calculating an indicated mean effective pressure for an engine having a predetermined structure. This equation uses predetermined frequency components of an in-cylinder pressure signal. In order to extract the predetermined frequency components of the in-cylinder pressure signal, the in-cylinder pressure signal is filtered by a first band-pass filter for extracting a fundamental wave component and a second band-pass filter for extracting higher harmonic wave components that are integral multiples of the fundamental wave component.
Patent application publication 1: No. H8-20339